1. Technical Field
The present invention relates to a method for controlling an exhaust gas purification system and the exhaust gas purification system for carrying out regeneration control including exhaust gas temperature rise control with post injection in order to recover the purification capacity of an exhaust gas purification device provided with a DPF for purifying components in the exhaust gas for an internal combustion engine such as diesel engines.
2. Background Art
Regulations on emissions of particulate matter (PM: particulate matter: hereinafter, referred to as the PM) as well as NOx, CO, HC and the like exhausted from diesel engines have been tightened year by year. Technologies have been developed in which a filter called as a diesel particulate filter (DPF: Diesel Particulate Filter: hereinafter, referred to as the DPF) traps the PM to reduce the PM amount exhausted to the outside. A continuous regeneration type DPF device carrying a catalyst are among them.
In this continuous regeneration type DPF device, when an exhaust gas temperature is approximately 350° C. or above, the PM trapped by the filter is continuously burned and purified, and the filter is self-regenerated. However, when the exhaust temperature is low, for example, when the sate in a low exhaust temperature is continued such as in cases of an idling operation, a low-load/low-speed operation or the like of the internal combustion engine, the exhaust gas temperature is low and a temperature of a catalyst is lowered and not activated, and thus, oxidization reaction is not promoted. Then, it becomes difficult to oxidize the PM and to regenerate the filter. As a result, the accumulation of the PM on the filter continues and the clogging of the filter progresses, resulting in a problem of exhaust pressure rise due to the clogging of the filter.
One method to solve such a problem is regeneration control for forcedly burning and removing the trapped PM by forcedly raising the temperature of the exhaust gas when the clogging of the filter exceeds a predetermined amount. Methods for detecting the clogging of the filter include a detection method using a differential pressure before and after the filter and a detection method by calculating a trapped PM amount from an engine operation state using a preset map data and the like so as to acquire an accumulated amount of the PM.
In this regeneration control, the exhaust gas temperature rise control is executed so that the temperature of the exhaust gas flowing into the filter may be raised to not less than a temperature at which the PM trapped by the filter is burned. Thus, the filter temperature is raised and the PM is burned and removed so that the filter is regenerated.
This kind of exhaust gas temperature rise control includes methods carrying out multiple injection (multi-stage delayed injection) or post injection in-cylinder fuel injection as described in Japanese patent application Kokai publication No. 2003-155917, Japanese patent application Kokai publication No. 2005-171841, Japanese patent application Kokai publication No. 2005-76604, and Japanese patent application Kokai publication No. 2004-225579, for example.
The multi injection is a delayed multi-stage injection in which the fuel in the cylinder is burned in many stages. By the multi injection, a fuel amount burned without work in the cylinder is increased, and the temperature of the exhaust gas exhausted from the cylinder, that is, the temperature of the exhaust gas flowing into an oxidation catalyst device can be raised to not less than a catalyst activation temperature of the oxidation catalyst. The post injection is injection for auxiliary injection at timing further delayed from the multi injection after main injection in the in-cylinder injection. By the post injection, HC (hydrocarbon) is increased in the exhaust gas exhausted from the cylinder and the HC is burned by the oxidation catalyst, by which the temperature of the exhaust gas on a downstream of the oxidation catalyst device can be raised.
On the other hand, in view of a measure against oil dilution that an unburned fuel is mixed with engine oil (lubrication oil) by the post injection and dilutes the engine oil, there is a control of forced regeneration executed during parking and idling in which the operation state is stable. In this control, when a predetermined amount of the PM is accumulated in the filter device, need for regeneration control of the filter device is notified to an operator (driver) by an alarm lamp or the like. When the driver having received the notification stops the vehicle and presses a manual regeneration button, a manual regeneration mode is started and the forced regeneration is operated.
In this system, by installing the oxidation catalyst device on a front stage (upstream side) of the filter device and by burning the HC supplied into the exhaust gas by the post injection in the oxidation catalyst device, the temperature of the exhaust gas at an inlet of the filter device is raised, thus executing the forced regeneration.
In this exhaust gas temperature rise, first, when the temperature of the exhaust gas is low as in the low-speed/low-load operating state, the multi injection is carried out for raising the exhaust gas temperature flowing into the oxidation catalyst device to the catalyst activation temperature of the oxidation catalyst. After the exhaust gas temperature has been raised, the exhaust gas temperature is kept at the catalyst activation temperature or above by the in-cylinder fuel injection control in which post injection is used in addition to the multi injection, while the post injection is executed and the HC is supplied to the oxidation catalyst device. Since the HC is oxidized by the oxidation catalyst to generate heat, the exhaust gas flows into the filter device with the temperature further raised. By the exhaust gas having a high temperature, the PM accumulated in the filter device is burned and removed.
However, in this manual regeneration control, since the vehicle is in a parked state, a cooling effect for the engine by a radiator is low. Thus, a temperature of a cooling water of the engine rises. Particularly, when heat radiated from a radiation portion of an air conditioner affects the radiator due to an arrangement relation between the radiation portion of the air conditioner and the radiator of the engine, it is highly likely that overheat of the engine may be caused when manual regeneration and use of the air conditioner are carried in the same time.
Then, a measure of stopping the operation of the air conditioner during the manual regeneration is employed, but that gives a sense of discomfort to a driver in summer, resulting in a problem that merchantability is extremely lowered.